Root Rot , or pythium, or damping off, is a bacteria which feasts on dead root material climbing up the plant and eventually choking it out at the base of the stem. To get rid of it what I did was clean and rinse reservoirs, added only H2O and H2O2, rinsed off the roots removing what was dead, and if already on the stem, removed all black colored tissue and rubbed a small amount of rubbing alcohol on my fingers and over the wound. Some plants that had the bugs feasting on it longer due to an unexpected trip, had to be chopped above the infection and re-rooted; during the worst episode I lost 6 ladies total. After wards I found that enzyme solutions (like the brand name ones the nutrient companies dilute and sell for twice the price of gold or the pond and pet store brands that seem to work just as well) do a great job of 'eating' away dead root material hence not providing the adequate environment to flourish. To prevent root rot keep your reservoir temperatures in check, make sure no moisture is collecting above the root zone, near the stems, on top of the neoprene, etc. and use some enzymes to keep your rotting roots to a minimum.
Brown Algae, a clear like slime, that sometimes can begin as a frothy white foam, soon turns to a brown almost gray muck, that can also leave what looks like oil slicks on the top of the water in your reservoir (coincidently, brown algae has been used to bioengineer a new type of fuel). This stuff can appear in reservoirs even with good temps, they can be caused by over feeding or higher than normal levels of nitrogen, exposure to HID, any many other scenarios. This stuff gets nasty and can choke out your stems. Getting rid of this puppy can be a pain, although I started when I first discovered the frothy foam and beat it first attempt, beginners luck I guess. To get rid of it I removed the plants from the reservoir, these were actually in a 14 gallon 6 hole DWC, I rinsed each of the plants' roots under the faucet with cool, not cold water, I then took a brand new reservoir (Rubbermaid containers are cheap for the most part, I have learned as a rule of thumb always keep at least one extra one around - and that's a tip from your uncle Lar) filled it with only H2O and H2O2 and let it run for 24 hours. I then rinsed the plan't roots under the faucet while the reservoir got bleached scrubbed and air blown dry. Added H2O, after 24 hours more with no sign of the slime I added nutes and continued as scheduled. There are a couple of products out there to combat the slime, with Physan 20 being one of the most recommended. As always to prevent, keep light away from water, rinse, drain, and replenish nutes at least every 2 weeks to prevent nitrogen build up, and keep your grow areas as clean as humanly possible - remember what mom used to say, "I wan't this floor clean enough to eat off of!" If you wouldn't eat off any surface in your grow room then it's time to clean it =)
